9/24: Memory & Storage • ROM • RAM – different kinds & uses inc. VRAM, SRAM • Data storage – Magnetic – Optical image courtesy of How Computers Work CD
Jan 22, 2016
9/24: Memory & Storage
• ROM
• RAM– different kinds &
uses inc. VRAM, SRAM
• Data storage– Magnetic– Optical
image courtesy of How Computers Work CD
ROM? RAM?
• Both refer to chip-based memory hardware – (not hard drives, CD-ROMs, etc.)
• ROM: Read-Only Memory– doesn’t change (much if at all)– BIOS stored here.
• RAM: Random Access Memory– changes frequently– short-term memory
ROM: Read-Only Memory
• Chips hardwired with start-up instructions
• Nonvolatile memory– doesn’t change
• Non-dynamic– not dependent on
electrical power to store information
• Necessary to start up the operating system (OS)
• Has a few options: disk drive boot order, etc.
RAM: Random Access Memory
• Synonyms: “main memory”, “primary memory”, “user memory”
• Volatile memory– contents can be changed
• Why “random access”?– sequential access vs. random access– analogy: cassette vs. CD
• Programs, files stored here while in use.
image courtesy of How Computers Work CD
How much RAM do you need?
• Current recommendation: 192 MB total RAM for a new computer
• Windows 98 uses ~ 20 MB of RAM
• Windows 2000 Pro uses ~ 95 MB of RAM
• McAfee Virus Scan & Task Manager ~ 7 MB
• MS Word uses ~ 7 MB
• MS Internet Explorer uses ~ 7 MB
• Each file you open is held in RAM, even after you close it
Varieties of RAM: DRAM
• DRAM: Dynamic RAM– dynamic: needs electricity to hold data. Must be
continually replenished with electricity.– FPM: Fast Page Mode– EDO: Extended Data Out
• can send data while receiving other data
– BEDO: Burst EDO• sends “pipelined” data, speeding up EDO
– SDRAM: Synchronous DRAM• runs at the CPU clock speed (faster than prev. types)
• today’s main DRAM.
Variety of RAM: SRAM
• SRAM: Static RAM– static: does not need to be continually refreshed.– more expensive, bigger, and faster than DRAM.– used in CPU chips (caches)– used in “flash memory”
image courtesy of Sonystyle.com
DRAM: Configurations
• Memory modules
• SIMMs - 32-bit, require pairing on Pentium systems
• DIMMs - 64-bit, do not require pairing on Pentium systems
image courtesy of gamespot.com
How RAM works
• RAM chips have millions of transistor/capacitor pairs.
• Capacitors can briefly hold an electric charge.
• Gates are opened and closed by the address lines.
• Data goes in andout on the data lines
Address Line
Data Line
Capacitor
Transistor
image courtesy of How Computers Work CD
Data storage: what is it?
• Long-term storage, not immediate memory
• Not RAM (short-term memory)
• Synonyms: secondary storage, auxiliary storage, mass storage
images courtesy of dalelabs.com,, iomega.com, imation.com,
Data storage: where is it?
• Storage involves 2 parts: the device & the media
• Removable vs. fixed media
• Where can you store data?– magnetic media– optical media– magneto-optical media– solid state media
image courtesy of How Computers Work
Storage characteristics• Random vs. sequential access• Tracks & sectors• Speed
– spin rate (RPM)– seek time & latency– access time– data transfer rate
• Storage Capacity– areal density– size
Image courtesy of How Computers Work
Magnetic data storage
• Use magnets to store bits:– example: 0 = N , 1 = S
• Reading and writing
• Floppy disk drives
• Hard disk drives
PACE
image courtesy of How Computers Work
Floppy disk drives: types
• Low-density floppy drives: 5.25” floppy disks3.5” 1.44 MB floppy disks
• High-density floppy drives: Zip disks, LS-120 disks
Images courtesy of How Computers Work, Imation.com, and Iomega.com
Floppy disk drives: how they work• Shutter opens with an arm.• Cookie spins on the spindle.• Read/write heads get close
to the cookie inside• Magnetic particles generate
electric currents in the heads.
• Electric currents are interpreted as a series of bits.
Images courtesy of How Computers Work
Hard disk drives: overview
• Glass platters coated with magnetic particles
• Read/write heads like floppy drives but much smaller
• Multiple platters, multiple heads.
Image courtesy of How Computers Work
Hard disk drives: how they work
• Platters spin on the spindle.
• Heads move over the platters.
• To read, magnetic particles generate currents in the heads.
• Electric currents are interpreted as a series of bits.
• To write, the electric currents manipulate the magnetic particles on the platters.
Images courtesy of How Computers Work
Optical Storage• Instead of using magnetism to store bits, we use light• A laser is the light
– Laser: “light amplification by stimulated emission of radiation”
– Extremely focused, narrow beam of powerful light– Depending on the wavelength, the beam can be narrower or
wider
• Lands are flat areas on the disc– Reflect light like a mirror
• Pits are holes in the disc– Scatter light
Courtesy of http://www.microserve.net/~tpetchy/DVD.shtml
CD Drives: Types and Operation
• CD-ROM drive speeds: how many times faster than the original CD-ROM drives• 2x, 4x, 6x, 8x, 16x, 32x, 48x
• Operation:• Diode generates laser• Laser bounces off mirrors, reaching the disc• Disc reflects or scatters laser• Light-sensing diode sees the reflections, comparing
them to a timing circuit to generate 0s and 1s
Image courtesy of c-cube.com
Types of Optical Discs
• Compact discs:– CD-ROM: read only memory (680 MB)– CD-R: Recordable (650 MB)– CD-RW: ReWritable (495 MB)
Image courtesy of c-cube.com
Types of Optical Discs• Digital versatile discs – higher density storage
– DVD-ROM: read only memory (4.7 – 17 GB)– DVD-R: Recordable (3.9 GB?)– DVD-ram (5.2 GB) & DVD+RW (6.0 GB): Rewritable
(still fighting)
Image courtesy of c-cube.com